Method for manufacturing an aluminum tube

ABSTRACT

The invention relates to a method for manufacturing an aluminum tube, an aluminum tube for further processing in at least one subsequent deformation process, as well as the use of the aluminum tube. The object of providing a simple method for manufacturing an aluminum tube with elevated deformation potential is solved by texturing the outer surface of the aluminum tube using temper rolls. The application of a texture using temper rolls yields a sufficiently high roughness on the surface of the aluminum tube on the one hand, so that the strain can be increased in subsequent deformation processes. On the other hand, while the roughening of the surface can be integrated into existing manufacturing processes, e.g., for straight bead welded or extruded aluminum tubes a swift and easy manufacture of the semi-finished product is enabled.

[0001] The invention relates to a method for manufacturing an aluminum tube, an aluminum tube for further processing in at least one subsequent deformation process, as well as the use of the aluminum tube.

[0002] The use of straight bead welded or extruded aluminum tubes as semi-finished products in subsequent deformation processes is known in the art, for example. In particular hydroforming makes it possible to use aluminum tubes for manufacturing components with a complex shape, e.g., for the chassis of a motor vehicle. The manufacturing process yields a very smooth outside surface for the straight bead welded and extruded aluminum tubes, with a roughness in the longitudinal direction of under Ra=0.1 μm. However, this results in an elevated friction on the deformation tool during hydroforming. For this reason, only low strains can be achieved during hydroforming. In addition, manufacturing defects can arise in critical deformation areas of the semi-finished product, so that a flawless production process cannot be ensured. If high strains are required, the aluminum tubes must either be coated or their surface roughened by surface blasting before machining. Both steps result in a considerable cost and time effort in the production process.

[0003] Known in conventional sheet deformation processes, e.g., deep-drawing, is to apply a precisely defined texture to the strip surface by re-rolling the flat strip stock in order to maximise the strain without cracking, that means to maximise the deformation potential, while deep-drawing The increased strain results from the roughness recesses present in the texture of the strip stock, which serve as lubricant reserves during deformation, so that enough lubricant can be made available during critical deformation processes. To this end, the roughness recesses are engraved into the strip via temper rolls in a re-rolling just before the actual deformation process. Proceeding from the prior art described above, the object of this invention is to provide a simple method for manufacturing an aluminum tube with elevated deformation potential or a corresponding aluminum tube for further processing in at least one subsequent deformation process, and to propose a preferred application for the aluminum tube.

[0004] According to a first teaching of the invention, the object derived and described above is solved from a procedural standpoint in that the outer surface of the aluminum tube is textured by means of temper rolls.

[0005] Applying a texture with temper rolls yields a sufficient roughness on the surface of the aluminum tube on the one hand, so that the strain in subsequent deformation processes can be increased. On the other hand, surface roughening can be integrated into existing manufacturing processes, e.g., for extruded or straight bead welded aluminum tubes thereby enabling a swift and simple manufacture of the aluminum tube. Basically separate temper rolls or those integrated into the cold-rolling process and acting on the aluminum strip for straight bead welded aluminum tubes can be used as temper rolls, or all rolls used for roll forming, bending rolls or calibrating rolls.

[0006] If temper rolls are used with a surface machined according to the “electrical discharge texturing” (EDT) procedure or the “lasertex” (LT) procedure, the surface can be roughened with a high level of reproducibility according to a first embodiment of this invention. In the EDT procedure, electrodes are moved radially toward the rotating roll surface, and oscillated in an axial direction. An eroding pulse generates particles in the dielectric between the roll and electrode to a dipole bridge, and current flows. A small area of the roll surface is melted, and a gas bubble forms in the A dielectric. The gas bubble implodes after the eroding pulse is deactivated, and the melted roll material is thrown out. The roughness can therefore be varied independently of the roll hardness using parameters like voltage, control times and distance of electrodes. Regardless of the roll hardness, the roll surface can also be textured using the LT procedure. In the LT procedure, a laser beam is focused on the roll, which melts a small area of the surface. A chopper wheel interrupts the laser beam, wherein the pressure of the plasma and an inert gas blow out the melt. In this case, the melt either builds up to form a bead around the crater edge, or accumulates on one side of the crater, solidifying there. The surface roughness can here be adjusted via laser power, axial advance of the roll, and radial speed of the roll and the chopper. Temper rolls with a high roll hardness whose surface has been roughened by one of the aforementioned procedures are particularly advantageous, since they have an especially high service life in the process of temper rolling. In addition, “electron beam texturing” (EBT) and “shot blast texturing” (SBT) procedures are also known as possible texturing procedures.

[0007] If a straight bead welded aluminum tube is textured and the texture is engraved before deformation in a next embodiment of the method according to the invention, an already textured strip stock can be used as the raw material in existing production facilities for manufacturing the semi-finished product.

[0008] In another embodiment of the method according to the invention, the texture of the outer surface of the straight bead welded aluminum tube is altered the least by ensuing rolling processes if the texture is alternatively or cumulatively engraved before calibration rolling or during calibration procedure.

[0009] In addition, it is possible in another advantageous configuration of the procedure according to the invention to incorporate the texture after finishing the straight bead welded aluminum tube, or immediately prior to the next deformation step, by alternatively or cumulatively engraving the texture after the calibration rolling.

[0010] According to the second teaching of the invention, the previously derived object for an aluminum tube for further processing in at least one ensuing deformation process is solved in that the outer surface of the aluminum tube has a texture. The surface roughness reduces the friction coefficients between the work piece and deformation tool in subsequent deformation processes. Due to the elevated deformation potential of the aluminum tube, the overall deformation behavior in subsequent deformation processes is improved, so that the process safety can be distinctly increased during deformation.

[0011] In a next further developed embodiment of the aluminum tube according to the invention, a reliable deformation can be ensured in critical deformation areas in that the texture comprises roughness valleys and/or lubricant pockets for holding lubricants. In addition, the lubricant quantity used during deformation can be reduced, if necessary.

[0012] If the texture has cup-like recesses, a next embodiment of the aluminum tube makes it possible to provide lubricant reservoirs on the surface of the aluminum tube in a particularly easy manner.

[0013] Especially good deformation properties can be achieved in a subsequent hydroforming procedure if the outer surface has an elevated surface roughness relative to temper-rolled semi-finished sheet metal products in another advantageous embodiment of the aluminum tube according to the invention. In particular, this step makes it possible to take into account the increased surface pressure during hydroforming.

[0014] According to the third instruction of the invention, the increased deformation potential of the aluminum tube and resultant high process safety during subsequent deformation process makes it particularly advantageous to use the aluminum tube according to the invention in a hydroforming procedure.

[0015] There are numerous ways in which to configure and further develop the method according to the invention for manufacturing an aluminum tube according to the first teaching of the invention, the aluminum tube according to the second teaching of the invention, as well as the application of the aluminum tube according to the third teaching of the invention. To this end, reference is made to the claims following claims 1 and 5 on the one hand, and to the description of an exemplary embodiment in conjunction with the drawing.

[0016] The sole FIGURE on the drawing diagrammatically shows the texture of a section of the outer surface of an exemplary embodiment of an aluminum tube manufactured with a method according to the invention.

[0017] The FIGURE diagrammatically shows a section 1 of the outer surface of an aluminum tube according to the invention with a texture 2 comprised of numerous cup-like recesses 3. The texture 2 was here engraved onto the outer surface of a straight bead welded aluminum tube by means of a temper roll textured with the LT procedure. The cup-like recesses 3 additionally have recessed lubricant pockets 4, which stem from beads located on the roll surface. In the LT procedure, the beads are generated by briefly melting the roll material. In this case, the roll material melted in the crater area is deposited in a bead while hardening at the edge of the crater.

[0018] The lubricant applied to the surface of the semi-finished product before an ensuing deformation step can be stored in the correspondingly introduced cup-like recesses 3 and lubricant pockets 4 on the surface of the semi-finished product. If the lubricant pockets 4 and/or cup-like recesses 2 are stretched or compressed in a deformation process, the lubricant contained therein can exit in the gap between the semi-finished product and deformation tool wall, and its friction coefficients can be kept low even given intense deformation. This clearly facilitates in particular the deformation of critical areas with elevated strain, so that the potential for dimensionally changing the aluminum is improved, and production safety can be significantly enhanced, in particular during hydroforming, 

1. A method for manufacturing an aluminum tube, characterized in that the outer surface of the aluminum tube is textured by means of the temper rolls.
 2. The method according to claim 1, characterized in that temper rolls are used with a surface machined according to the EDT or lasertex procedure.
 3. The method according to claim 1 or 2, characterized in that a straight bead welded aluminum tube is textured, and the texture is engraved prior to form rolling.
 4. The method according to claim 3, characterized in that the texture is engraved alternatively or cumulatively before calibration rolling or during calibration rolling.
 5. The method according to claim 3 or 4, characterized in that the texture is engraved alternatively or cumulatively after calibration rolling.
 6. An aluminum tube for further processing in at least one ensuing deformation procedure, in particular manufactured using a method according to one of claims 1 to 5, characterized in that the outer surface (1) of the aluminum tube has a texture (2).
 7. The aluminum tube according to claim 6, characterized in that the texture (2) has roughness valleys and/or lubricant pockets (4) for storing lubricants.
 8. The aluminum tube according to claim 6 or 7, characterized in that the texture (2) has cup-like recesses (3).
 9. The aluminum tube according to one of claims 6 to 8, characterized in that the outer surface has an elevated surface roughness relative to temper rolled semi-finished sheet metal products.
 10. Use of an aluminum tube according to one of claims 6 to 9 in a hydroforming procedure. 